U.S. patent number 6,597,988 [Application Number 09/960,828] was granted by the patent office on 2003-07-22 for network assisted pseudolite acquisition for enhanced gps navigation.
This patent grant is currently assigned to SiRF Technology, Inc.. Invention is credited to Keith Jacob Brodie, David Allan Tuck.
United States Patent |
6,597,988 |
Brodie , et al. |
July 22, 2003 |
Network assisted pseudolite acquisition for enhanced GPS
navigation
Abstract
The invention comprises a set of pseudolites deployed throughout
an area of interest in which the GPS constellation visibility may
be limited, such as in and around some high-rise buildings in an
urban setting, and a database of these installed pseudolite
locations with their PRN numbers indexed by cell-site. When the
cellular telephone is in communication with a particular tower or
transceiver, the PRN numbers of all local psuedolites are
transmitted to the cellular telephone. If the cellular telephone
has a position solution which has been transmitted to the cell
tower, prepositioning information for a code search can be
transmitted to the phone as well. The phone can then augment the
phone's normal acquisition list with the psuedolites in the area
and track the pseudolites to augment navigation capabilities in a
harsh environment.
Inventors: |
Brodie; Keith Jacob (Irvine,
CA), Tuck; David Allan (El Segundo, CA) |
Assignee: |
SiRF Technology, Inc. (San
Jose, CA)
|
Family
ID: |
26928334 |
Appl.
No.: |
09/960,828 |
Filed: |
September 21, 2001 |
Current U.S.
Class: |
701/469;
342/357.75; 342/357.77; 701/484 |
Current CPC
Class: |
G01C
21/28 (20130101); G01S 19/11 (20130101); G01S
5/0045 (20130101); G01C 21/206 (20130101); G01S
19/258 (20130101) |
Current International
Class: |
G01S
5/14 (20060101); G01S 5/00 (20060101); G01C
21/28 (20060101); G01C 001/00 () |
Field of
Search: |
;701/213,214,215,216,207
;342/357.01,357.02,357.03,357.06,357.08,357.12 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Camby; Richard M.
Attorney, Agent or Firm: Hogan & Hartson, LLP
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims priority under 35 U.S.C. .sctn.119(e) of
U.S. Provisional Patent Application No. 60/234,856, filed Sep. 22,
2000, entitled "NETWORK ASSISTED PSEUDOLITE ACQUISITION FOR
ENHANCED GPS NAVIGATION," by Keith J. Brodie et al., which
application is incorporated by reference herein.
Claims
What is claimed is:
1. An enhancement system for a Satellite Positioning System
(SATPS), comprising: at least one pseudolite deployed in a
geographical region of interest; a database comprising a
geographical position related to each of the deployed pseudolites;
means for communicating at least a portion of the database
comprising the geographical position of the deployed pseudolites to
a SATPS receiver for use in determining a position of the SATPS
receiver.
2. The enhancement system of claim 1, wherein the deployed
pseudolite are deployed in a geographical region that has a limited
SATPS constellation visibility.
3. The enhancement system of claim 2, wherein the database is
indexed.
4. The enhancement system of claim 3, wherein the database is
indexed by cellular telephone system cell site.
5. The enhancement system of claim 4, wherein the SATPS system is a
Global Positioning System (GPS).
6. The enhancement system of claim 5, wherein the means for
communicating is a cellular telephone system.
7. The enhancement system of claim 6, further comprising means for
transmitting the geographical position of the deployed pseudolites
to the cellular telephone system.
8. The enhancement system of claim 7, further comprising
transmitting prepositioning information for a code search from the
cellular telephone system to the SATPS receiver.
9. The enhancement system of claim 5, wherein the means for
communicating is a one-way broadcast mechanism.
10. The enhancement system of claim 9, wherein the one-way
broadcast mechanism is an FM broadcast station.
11. An interface to a Satellite Positioning System (SATPS)
receiver, comprising means for inputting local pseudolite
information, wherein the local pseudolite information is
selectively used by the SATPS receiver for determining geoposition
of the SATPS receiver, and wherein the interface is separate from a
SATPS antenna input used for receiving SATPS signals.
12. The interface of claim 11, wherein the local pseudolite
information comprises a pseudolite PRN number and a geographical
location of the pseudolite.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to Satellite Positioning
System (SATPS) receivers, and in particular to a network assisted
pseudolite acquisition for enhanced SATPS navigation.
2. Description of the Related Art
Cellular telephony, including Personal Communication System (PCS)
devices, has become commonplace. The use of such devices to provide
voice, data, and other services, such as internet access, has
provided many conveniences to cellular system users.
A current thrust in the cellular and PCS arena is the integration
of Global Positioning System (GPS) technology, which is a subset of
SATPS technology, into cellular telephone devices and other
wireless transceivers. For example, U.S. Pat. No. 5,874,914, issued
to Krasner, which is incorporated by reference herein, describes a
method wherein the basestation (also known as the Mobile Telephone
Switching Office (MTSO)) transmits GPS satellite information,
including Doppler information, to a remote unit using a cellular
data link, and computing pseudoranges to the in-view satellites
without receiving or using satellite ephemeris information.
This current interest in integrating GPS with cellular telephony
stems from a new Federal Communications Commission (FCC)
requirement that cellular telephones be locatable within 20 feet
once an emergency call, such as a "911" call (also referred to as
Enhanced 911 or "E911") is placed by a given cellular telephone.
Such position data assists police, paramedics, and other law
enforcement and public service personnel, as well as other agencies
that may need or have legal rights to determine the cellular
telephone's position. Further, GPS and/or SATPS data can be used by
the cellular user for directions, location of other locations that
the cellular user is trying to locate, determination of relative
location of the cellular user to other landmarks, directions for
the cellular user via internet maps or other GPS/SATPS mapping
techniques, etc. Such data can be of use for other than E911 calls,
and would be very useful for cellular and PCS subscribers.
However, since cellular telephones can travel into areas where
SATPS signals cannot be reliably received, augmentations to the
SATPS system are being researched to support the E911 and other
SATPS/cellular applications. SATPS is increasingly being pressed
into service in the cellular telephone/PDA/mobile computer
application where a solution is required in areas with substantial
blockage, such as inside buildings, in subway stations, and other
areas where the system RF link budget is unable to sustain
communications with mobile units that travel into hostile signal
reception environments such a buildings. Pseudolites are well-known
commercially available ground-based transmitters which augment the
orbiting SATPS constellation with one or more additional
transmitters to improve the availability and quality of a SATPS
solution. Current pseudolite applications include local-area
augmentation system (LAAS) transmitters for precision approach.
It can be seen, then, that there is a need in the art for a method
and apparatus for assisting the cellular network in locating
cellular telephones. It can also be seen that there is a need in
the art for a method and apparatus for assisting the network in
locating cellular telephones in hostile signal environments such as
buildings. It can also be seen, then that there is a need in the
art for methods and apparatuses for assisting a mobile user in a
harsh signal environment using extra-network devices such as
pseudolites.
SUMMARY OF THE INVENTION
To minimize the limitations in the prior art, and to minimize other
limitations that will become apparent upon reading and
understanding the present specification, the present invention
discloses methods and apparatuses for assisting the cellular
network, or other type of network, with SPS acquisition, tracking,
and navigation using extra-network devices such as pseudolites.
The invention comprises a set of pseudolites deployed throughout an
area of interest in which the SATPS constellation visibility may be
limited, such as in and around some high-rise buildings in an urban
setting, and a database of these installed pseudolite locations
with their PRN numbers indexed by cell-site. When the cellular
telephone is in communication with a particular tower or
transceiver, the PRN numbers of all local psuedolites are
transmitted to the cellular telephone. The data transmitted for
each pseudolite could be simply the pseudolite ID, the ID and
position of the pseudolite, or the ID and the complete data message
for the pseudolite (which would include it's position). The phone
can then augment the phone's normal acquisition list with the
psuedolites in the area and track the pseudolites to augment
navigation capabilities in a harsh environment. The advantage of
having the pseudolite ID's transmitted to the SATPS receiver for
addition to the acquisition list is that they are usually not
looked for at all, because they are infrequently available. In GPS,
for example, pseudorandom code numbers (PRNs) 1 to 32 are reserved
for space vehicles, and PRNs 33 through 37 are reserved for
pseudolites. Since pseudolites are local area transmitters, these
PRNs may be reused in different geographic areas without
interference. A conventional GPS receiver, however, would not
search ID's 33 through 37 for potential pseudolites because of
their deployment is very rare. Searching for transmitters that have
not been deployed wastes power and time in the GPS receiver. The
present invention extends the conventional SATPS system by
providing the list of available pseudolite PRNs to SATPS systems
which may benefit from tracking them because of the obstructed
signal environment.
The position of the pseudolite may be transmitted by the cell base
station as well. If the position is transmitted, it can be used by
the SATPS to compute a prepositioning range and range-rate for the
pseudolite for faster acquisition of the pseudolite signal.
Alternatively, if the cellular telephone has a position solution
which has been transmitted to the cell tower, prepositioning
information for a code search can be transmitted to the phone. If
the pseudolite position and any required clock correction terms are
transmitted by the cell base station to the SATPS receiver, then
the pseudolite pseudorange may be used in the SATPS navigation
computation before the pseudolite data message has been decoded
directly from the pseudolite transmission, thus making it available
for use in assisting navigation sooner. If all of the data in the
pseudolite data message is transmitted to the SATPS by the cell
base station, the data message in the actual pseudolite signal can
be stripped off of the incoming signal. In the case of a GPS
pseudolite, this allows coherent tracking of the pseudolite signal
beyond the 20 millisecond (ms) boundary normally imposed by the
data rate in the modulating bi-phase shift keyed (BPSK) code.
In another embodiment of the invention, the pseudolite information
is transmitted to the mobile user via a broadcast mechanism, with
no communication from the mobile user back to the source
transmitting the local pseudolite information. An FM broadcast
station sub-carrier would be well suited to this task, because the
limited range of the FM broadcast availability may be consistent
with the range of the signals transmitted by the pseudolites
identified in the FM sub-carrier broadcast. So, for example, in a
city with a local FM station, the sub-carrier broadcasts the ID
numbers of the pseudolites available in the city. As in the case of
the cellular network based system, the broadcast may also include
the pseudolite positions, the pseudolite clock corrections, or the
entire pseudolite data message. In any of these cases, the SATPS
receiver, augmented with the sub-carrier receiver, picks up the
ID's and any other pseudolite information, and is therefore able to
acquire, track, and navigate with signals from the local
pseudolites as well as the satellites. The resultant navigation
fixes may be for use locally by the mobile user, or they could be
transmitted to through another network, such as the cellular
telephone network, to support E911, fleet management, and other
applications. The mechanism for transmitting the pseudolite aiding
information can be one-way and need not be associated with the
transmission of navigation data from the mobile user.
It is an object of the present invention to provide a method and
apparatus for assisting the cellular network in locating cellular
telephones. It is another object of the present invention to
provide a method and apparatus for assisting the network in
locating cellular telephones in hostile signal environments such as
buildings. It is a further object of the present invention to
provide methods and apparatuses for assisting the network using
extra-network devices such as pseudolites.
BRIEF DESCRIPTION OF THE DRAWINGS
Referring now to the drawings in which like reference numbers
represent corresponding parts throughout:
FIG. 1 is a diagram showing the communication links and operation
of the invention for two different users connected to a single cell
tower; and
FIG. 2 illustrates a typical scenario using the present invention
in a different embodiment with the pseudolite data broadcast on an
FM sub-carrier.
DETAILED DESCRIPTION OF THE DRAWINGS
In the following description of the preferred embodiment, reference
is made to the accompanying drawings which form a part hereof, and
in which is shown by way of illustration a specific embodiment in
which the invention may be practiced. It is to be understood that
other embodiments may be utilized and structural changes may be
made without departing from the scope of the present invention.
Overview
The present invention is embodied in hardware and/or software that
is used to perform the computations described above. Different
embodiments of the invention may be used to perform different types
of calculations, e.g., a single integrated circuit or piece of
software can be used to perform the time ambiguity calculation, a
second integrated circuit or piece of software can be used to
perform the z-direction ambiguity calculation, or a single
integrated circuit or piece of software can be used to perform all
calculations described by the present invention. The apparatus is
not limiting to the applications of the present invention.
FIG. 1 is a diagram showing the communication links and operation
of the invention for two different users connected to a single cell
tower.
FIG. 1 illustrates a set of SATPS transmitters 1.a,b,c,d, such as
GPS satellites. The diagram also shows two pseudolites, one mounted
on the roof of a building 3, the second mounted inside of a
building 5. The satellites and pseudolite transmissions are
received by users. Two users are shown, a person with a
SATPS-equipped cellular telephone in a building 15, and a truck
with a SATPS receiver and cellular telephone transceiver onboard
13.
The users 13, 15 are in communication with a cell phone base
station indicated by the cell tower 7, the base station
transceivers(s) and controller(s) 11 and a pseudolite database 9.
The pseudolite database is maintained in a computer. It may be
maintained locally, as shown, or at some more centralized
location.
In operation, the user's 13,15 cellular telephone equipment
identifies itself as SATPS equipped and capable of tracking
pseudolites to the base station 11 over the communications links
19a and 19b. The base station obtains the list of pseudolites in
close range to the tower from the pseudolite database, and
transmits to the user equipment the ID codes of the pseudolites 3,5
deployed in the area. The transmitted pseudolite information may
include 1. the pseudolite ID's only; 2. the ID's and their
locations; 3. the ID's and the content of their entire data
message, including location. The SATPS receivers in the user
equipment 13,15, add the pseudolite ID's to their search lists, so
they can search for, acquire, and track the local pseudolites. If
the location information was transmitted, the pseudolite can be
used for navigation before the data is decoded. The pseudolite
signals provide for improved navigation, and may be sufficient to
compensate for signals lost for the indoor user 15.
Typical Scenario Using the Present Invention
FIG. 2 illustrates a typical scenario using the present invention
in a different embodiment with the pseudolite data broadcast on an
FM sub-carrier. Although a single scenario is illustrated, it is
understood that other scenarios are possible given the teachings of
the present invention. The scenario of FIG. 2 is for illustrative
purposes only, and is in no way intended to limit the scope of the
present invention.
In FIG. 2, the mobile user 208 is a receiving only user, i.e., user
208 cannot transmit signals to any other receiver. However, in
other scenarios, user 208 may have transmit capabilities. GPS
transmissions are being received from satellites 206a,b and from
pseudolites 202,210. An FM broadcast sub-carrier is being received
from the local FM station 200. The GPS transmission from another
satellite 204 is being blocked by a building 212, typical of a
harsh urban signal environment. The FM sub-carrier transmission has
identified the PRN numbers for the local pseudolites 202, 210, so
the GPS receiver at the mobile user 208 can add the pseudolites 202
and 210 to the search list, acquire the pseudolites 202 and 210,
and track them along with the GPS satellites 206a and 206b. The
process of satellite signal acquisition and tracking is described
in "Understanding GPS Principles and Applications," by Kaplan, pp
119-208 which is herein incorporated by reference.
The foregoing description of the preferred embodiment of the
invention has been presented for the purposes of illustration and
description. It is not intended to be exhaustive or to limit the
invention to the precise form disclosed. Many modifications and
variations are possible in light of the above teaching. It is
intended that the scope of the invention not be limited by this
detailed description, but by the claims appended hereto.
* * * * *